This invention generally relates to cathode ray tubes (CRTs) and, more particularly, to a tension mask frame assembly for CRTs having improved thermal expansion and warp characteristics.
A color cathode ray tube, or CRT, includes an electron gun for forming and directing three electron beams to a screen of the tube. The screen is located on the inner surface of the faceplate panel of the tube and is made up of an array of elements of three different color-emitting phosphors. A shadow mask, which may be either a formed mask or a tension mask having strands, is located between the electron gun and the screen. The electron beams emitted from the electron gun pass through apertures in the shadow mask and strike the screen causing the phosphors to emit light so that an image is displayed on the viewing surface of the faceplate panel.
One type of CRT has a tension mask comprising a set of strands that are tensioned onto a mask support frame to reduce their propensity to vibrate at large amplitudes under external excitation. A tension mask support frame assembly has been developed which includes a pair of support blade members which are welded or otherwise attached to a mask support frame. The tension mask is supported between these support blade members. In order to maintain a desired tension on the tension mask at elevated tube processing temperatures, it is desirable to have matched coefficients of thermal expansion (CTE) in the material which forms the support blade members and the material which forms the tension mask. Thermal expansion mismatch between these components has been found to cause undesirable anomalies in the tension mask surface occurring during the thermal cycling of tube processing. Although the support blade members and tension mask may be formed of matched relatively low CTE materials, such as INVAR, these materials tend to be relatively expensive. It is therefore desirable to form the mask support frame of a relatively inexpensive high CTE material such as steel. A problem occurs however in that where the support blade member having a low CTE is connected to the mask support frame having a high CTE, there is a thermal expansion mismatch. This thermal expansion mismatch causes deflection or warping of the support blade member in the Z-axis direction at elevated tube operating temperatures.
It is desirable to develop a mask frame assembly that allows the use of relatively lower CTE inexpensive material for the mask support frame assembly while preventing excessive Z axis deflection of the mask support blade members during the thermal cycling that occurs during normal CRT operation.
A tension mask frame assembly for use in a cathode ray tube is provided. The tension mask frame assembly includes a substantially rectangular mask support frame, having a first coefficient of thermal expansion. The frame is formed of a pair of opposing long sides being joined to a pair of opposing short sides wherein one of these pairs has an attachment zone. The tension mask, having a second coefficient of thermal expansion, is supported by the frame at the attachment zones along the opposing sides. The attachment zones are formed of a material having a coefficient of thermal expansion which is approximately the same as the second coefficient of thermal expansion in order to be matched with the tension mask expansion.